Understanding of DMX 512 Protocol

DMX 512 is a standard for digital communication networks that are commonly used to control stage lighting and effects.


It was originally intended as a standardized method for controlling light dimmers (light dimmer packs), which, prior to DMX 512, had employed various incompatible proprietary protocols. It soon became the primary method for linking controllers to dimmers (light dimmer packs) and special effects devices such as fog machines and intelligent lights.


DMX has also expanded to uses in non-theatrical interior and architectural lighting, at scales ranging from strings of Christmas lights to electronic billboards.




A DMX 512 network employs a multi-drop bus topology with nodes strung together in what is commonly called a daisy chain.


A network consists of a single DMX 512 controller which is the master of the network and one or more slave devices.


For example, a lighting console is frequently employed as the controller for a network of slave devices such as dimmers, fog machines and intelligent lights.


Each slave device has a DMX512 "IN" connector and usually an "OUT" (or "THRU") connector as well. The controller, which has only an OUT connector, is connected via a DMX 512 cable to the IN connector of the first slave. A second cable then links the OUT or THRU connector of the first slave to the IN connector of the next slave in the chain, and so on. For example, the diagram below is how I control a simple network consisting of a controller and three slaves (RGB LED Lights) using a laptop and software.


The specification requires a terminator to be connected to the final OUT or THRU connector of the last slave on the daisy chain, which would otherwise be unconnected. A terminator is a stand-alone male connector with an integral 120 Ω resistor connected across the primary data signal pair; this resistor matches the cable's characteristic impedance. If a secondary data pair is used, a termination resistor is connected across it as well. Although simple systems (i.e., systems having few devices and short cables) will sometimes function normally without a terminator, the standard requires its use. Some DMX slave devices have built-in terminators that can be manually activated with a mechanical switch or by software, or by automatically sensing the absence of a connected cable.
A DMX 512 network is called a "DMX universe". Each OUT connector on a DMX512 controller can control a single universe. Smaller controllers may have a single OUT connector, enabling them to control only one universe, whereas large control desks (operator consoles) may have the capacity to control multiple universes, with an OUT connector provided for each universe.